The present invention relates to a method for testing hydratable particle compositions, and more particularly to an automated assay method for testing hydratable cementitious compositions containing additives and/or admixtures and predicting physical or chemical properties of these compositions.
The terms xe2x80x9cadditivexe2x80x9d and xe2x80x9cadmixturexe2x80x9d are generally understood in the cement and concrete arts. The term xe2x80x9cadditivexe2x80x9d generally refers to an agent that is operative to increase grinding efficiency of cement clinker, to reduce the pack setting of processed cement, or otherwise to modify one or more properties or to increase efficiency of the cement grinding operation. The term xe2x80x9cadditivexe2x80x9d thus usually refers to any addition, such as a processing addition, which aids in the manufacture and handling of the cement product, or a functional addition that modifies the use properties of the cement. On the other hand, the term xe2x80x9cadmixturexe2x80x9d refers to a material other than water, aggregate (e.g., crushed stones or gravel, sand), and cement which might be added to concrete before or during its mixing. Admixtures can function by several mechanisms, such as (1) dispersions of the cement or particle in the aqueous phase of concrete (e.g., slurry); (2) alteration of the normal rate of hydration of the cement, in particular the tricalcium silicate phase; (3) reaction with the by-products of the hydrating cement, such as alkalies and calcium hydroxide; and (4) no reaction with either the cement or its by-products.
The terms xe2x80x9cadditivexe2x80x9d and xe2x80x9cadmixturexe2x80x9d sometimes overlap. It may be the case, within the present application, that the terms can be used synonymously in reference to agents for modifying cement, concrete, or other cementitious compositions, whether in dry particle, wet slurry (or paste), or hardened form (e.g., formed into a structure such as a foundation wall, block, brick, paver, etc).
To this point in the industry, the testing of additives and admixtures has involved production of relatively large mortar or concrete samples. A mortar or concrete sample would usually be made by mixing Portland cement with water and fine aggregate (in the case of mortar) or fine and coarse aggregate (in the case of concrete), after which an additive and/or admixture can be added. If the fluidity or slump properties were being measured, the cementitious composition would be poured into a standard slump cone (approximately one foot high). If the corrosion resistance were being tested, the sample would be cast into approximately 2-4xe2x80x3xc3x974-8xe2x80x3 cyclinders or 6xe2x80x3xc3x975xe2x80x3xc3x9712xe2x80x3 brick rectangles (or xe2x80x9cmini-beamsxe2x80x9d). If the compressive strength of mortar was being tested, two-inch cubes were made, and cylinders were made if the compressive strength of concrete were being tested. Thus, as a general proposition, the current techniques and methodologies in the industry for testing, analyzing, or evaluating one or more physical or chemical properties of cementitious materials, optionally containing additives or admixtures, typically involved large volumes of materials and laborious, time-consuming testing on a sample-by-sample basis.
In U.S. Pat. No. 6,009,419, Coveney and Fletcher describe a method for predicting the thickening (setting) time of a cement slurry from the Fourier transform infrared spectra (FTIR) of a cement powder or cement slurry. The thickening time of a cement slurry is of principal importance in the field of oilwell cementing and is dependent upon a number of properties including the mineral composition of the cement. However, the authors only practice a method for predicting the thickening time from the FTIR spectra of the cement powder. The FTIR spectrum of the unhydrated cement powder contains information on the cement composition and is also somewhat affected by other non-chemical properties, such as particle size distribution, crystallographic defects in cement grains, and compositional variations between cement grains, all of which may influence thickening times.
In the present invention, however, a method for predicting compressive strength of mortar is described which involves the analysis of Raman spectra of cement paste (hydrated cement powder or cement slurry) samples. This invention is fundamentally different from that in U.S. Pat. No. 6,009,419 in that (1) spectrum are being recorded of cement paste instead of cement powder, (2) thickening time and compressive strength are different physical properties (and it is believed by the present invenors that the ability to predict the former does not guarantee the ability to predict the latter), and (3) Raman spectroscopy as an analytical technique is fundamentally different from infrared spectroscopy.
Moreover, a particularly differentiating feature of the present invention from that described in the ""419 patent is that the present inventors found that the effect of additives on compressive strength could not be predicted from infrared spectra (specifically photoacoustic spectroscopy) of the cement paste (slurry). The present inventors discovered that Raman spectrum recorded on cement paste samples, unlike the infrared spectrum, did permit detection of differences in cement chemistry induced by additives which resulted in changes in compressive strength.
One objective of the present invention is to provide a novel and inventive methodology for rapid and cost-efficient discovery or improvement of additives and admixtures for hydratable cementitious compositions. Multiple formulations comprising hydratable cementitious compositions are deposited into a plurality of receptacles which are assayed by certain spectroscopic techniques. This first assay output value is used to predict, through a correlating model, a second assay output value corresponding to one or more physical or chemical properties of said cementitious compositions. The methodology is applicable to the analysis and optimization of the chemical and physical properties of mixtures of cement and water optionally containing fine aggregate and cement additives or concrete admixtures, but can also be applied to a multitude of formulated materials.
In particular, methodologies of the invention are useful for the analysis and optimization of physical or chemical properties of mixtures of cement and water optionally containing fine aggregate and cement additives or concrete admixtures. For example, automated techniques of the present invention are useful for producing milliliter-scale cement slurry (or paste) or mortar samples with or without additive(s) and/or admixtures(s). The automated techniques can produce an enormous volume (hundreds and even thousands) of slurry (or paste) or mortar samples per week. The cement paste or mortar samples may differ in accordance with variations as to cement type, water-to-cement ratio, fine aggregate type, additives or admixtures type (and/or amounts), and filler material type and/or amount. Exemplary samples of the invention may be provided as a plurality of receptacles (such as small cuvettes in a rack or tray) or be contained on a substrate (such as a cement slab, plastic tray, plexiglass or glass sheet having pockets or indentations for containing samples and can be of any size and shape (preferably cylindrical or cubical). Exemplary cement paste or mortar samples (with or without additives/admixtures) are analyzed (concurrently or in parallel) to ascertain one or more properties of the cement slurry, cement paste, or mortar. These properties may include, but are not limited to, chemical composition, crystallographic structure, particle size distribution, micro-rheology (such as plastic viscosity, yield stress, etc.), ultrasonic response, electrical response, and compressive strength, among others.
Exemplary spectroscopic techniques suitable for use in process of the invention comprise Raman spectroscopy, which is most preferred, and also other preferred techniques, including x-ray diffraction, x-ray fluorescence, calorimetry, thermal gravimetric analysis, differential thermal analysis, loss on ignition, nuclear magnetic resonance, scanning electron microscopy, impedance spectroscopy, and ultrasound, or combinations of the foregoing. Such spectroscopic analytical techniques may be conducted at discrete times or over time intervals. The samples may be analyzed at any age (with age defined as the time after the addition of water), but the preferred age is between 0 and 28 days, more preferably between 0 and 2 days, and more preferably between 0 and 1 day. The results of the analyses are then used to predict, through a correlating model, a second assay output value corresponding to one or more physical or chemical properties of the samples. The knowledge gained from this analysis is then used to formulate an optimal cement additive or concrete admixture system for a given application and desired set of physical or chemical properties.
An exemplary assay method of the invention for testing cementitious compositions thus comprises: combining a plurality (e.g., preferably more than 2 and preferably at least 12) of additives and/or admixtures with water in individual receptacles; adding hydratable particles (e.g., cement, fly ash, slag, or combination thereof) and optionally fine aggregate to these receptacles to make a slurry or mortar; mixing the contents simultaneously with individual, variable speed overhead mixers for a desired time period (e.g., 30 seconds); dividing each of the mixed slurries or mortars into several new, individual receptacles; curing (or aging) the slurry or mortar samples in a controlled environment (e.g., controlled temperature, humidity, atmosphere, etc.); assaying the aged (e.g., ranging from 0 to 28 days) slurry or mortar samples by one or more technique; and optionally predicting, through a correlating model, a second assay output value corresponding to one or more physical or chemical properties of the samples. The effect of the amounts of additives or admixtures may be tested for their effects in terms of varied predetermined amounts.
Further features and benefits of the invention are described in further detail hereinafter.